One of the major goals of the USPHS is the regional elimination of measles by the year 2000, a goal that is achievable due to an increase in immunization rates and implementation of a two dose schedule for measles vaccine. However, there are still some unanswered questions regarding optimal use of measles vaccines . For example, research is needed in order to understand the safest method for immunization of immunocompomised children, such as those with HIV infection, who could suffer serious disease as the result of measles infection or serve as a focus of persistent shedding and spread of measles virus that could impede eradication efforts. This laboratory participated in a clinical trial to evaluate measles immunization of HIV+ children. ACTG 225 was a multi-center , single-blinded, randomized clinical trial to assess the safety and immunogenicity of early two-dose measles vaccination at 6 and 12 months of age (EV) compared with conventional primary immunization at 12 months of age (CV) in HIV infected and uninfected infants. 110 infants were enrolled in regimen A (measles vaccine at 6 and 12 months) or regimen B (measles vaccine at 12 months) and stratified by HIV status (HIV- groups, A1[n=66) and B1[n=30] or HIV+ groups, A2[n=7] or B2[ n=7]). Enrollment into the study was discontinued in April, 1998 because accrual of HIV+ infants was low coincident with the increase use of anti-retroviral therapy in pregnant women in the US. Response to measles vaccine was measured by neutralization assay at study weeks 0, 6, 26 and 32. All HIV+ children had measles antibody titers < 25 by 6 months of age and 75% of HIV- infants were similarly susceptible. Seroconversion rates of HIV+ children who received EV were compared to HIV+ receiving CV: 3/4 (75%) HIV+EV children responded to MV when tested at 13 months of age compared to 4/4 (100%) HIV+CVs. Interestingly, 5/5 HIV+EV responded to the first dose of MV, however one child lost measles antibody prior to re-immunization and did not respond to the second dose when vaccinated at 12 months of age. 37/45 (82%) of HIV-EV children responded to MV while 13/13 (100%) of HIV-CVs responded. Although the geometric mean antibody titers of children receiving early measles vaccine was lower than the mean titer of children immunized at 12 months of age, these differences were not significant. No serious adverse affects were seen after EV or CV of HIV+ children including no decrease in CD4+ lymphocyte count or percentage of CD4 + lymphocytes. These data indicate that early measles immunization of HIV+ infants may help to protect this vulnerable population. An early vaccination schedule may have application in areas of the world where measles and HIV are cocirculating.